A novel index-coupled distributed feedback quantum cascade laser emitting at λ ∼ 4.8 μm is demonstrated by a sampled grating. The coupling coefficient can be almost controlled arbitrarily according to the duty cycle of sampled grating. The additional supermodes caused by the sampled grating can be strongly suppressed by choosing a small sampling period, so that the supermodes are shifted apart from the gain curve. Single-mode emission without any significant disadvantages compared with uniform grating is achieved. Especially, this powerful approach presented here can be applied to achieve the performance with high power and low threshold simultaneously.